function animate(obj,target,callback){
    clearInterval( obj.timer);
    obj.timer = setInterval(function(){
        var step = (target - obj.offsetLeft)/10 ;
        step = step > 0 ? Math.ceil(step)  :  Math.floor(step) ;
        if( obj.offsetLeft == target){
            clearInterval(obj.timer);
            if(callback){
                callback()
            }
        } else{
            obj.style.left = obj.offsetLeft + step + 'px';
        }
        // obj.style.left = obj.offsetLeft + step + 'px';
    } ,30);
    
}